Conventionally, in order to increase a precision of route guidance of a navigation apparatus, the navigation apparatus updates map data by performing a data communication with a data center. Recently, the navigation apparatus can partially update map data in order to update only a part of the map data, which has been changed.
The map data is indicative of a map of an area. The map data is divided into one or more predetermined segment data elements, which are indicative of one or more predetermined segments included in the map of the area. Hereinafter, the predetermined segment is also referred to as a mesh, and the predetermined segment data element is also referred to as a mesh data element. When updating the map data by the data communication between the navigation apparatus and the data center, update data of the segments, which is to be updated, is transmitted from the data center to the navigation apparatus in units of a mesh data element, that is, per mesh data element. Hereinafter, a segment, whose segment data element is to be updated, is also referred to as a target segment or a target mesh, and the segment data element is also referred to as a target segment data element or a target mesh data element. Thus, when the number of the target segment data elements increases, amount of the update data of the target segments increases. Accordingly, a time period for obtaining the update data increases, and communication fee increases.
Regarding the foregoing difficulties, various technologies for partially updating the segment data elements according to a need of a user are disclosed, for example, in JP-4409431-B2 (corresponding to US 2006/0173614 A1), JP-4603735-B2 (corresponding to US 2003/0045997 A1), JP-3871311-B2 (corresponding to US 2003/0144792 A1), and JP-2003-75163-A. For example, in JP-4409431-B2 (corresponding to US 2006/0173614 A1), update data of only the target segments, which include a guidance route to a destination set by a user, is transmitted from the data center.
In a conventional technology, when a communication-disabled region, where the data communication is disabled, is included in the target segments, a further route guidance is not available after entering the communication-disabled region included in the target segments.